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Shear-driven magnetic buoyancy in the solar tachocline: The mean electromotive force due to rotation

Lookup NU author(s): Dr Craig Duguid, Professor Paul BushbyORCiD, Dr Toby Wood

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This is the final published version of an article that has been published in its final definitive form by Oxford University Press, 2023.

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Abstract

The leading theoretical paradigm for the Sun’s magnetic cycle is an alpha-omega-dynamo process, in which a combination of differential rotation and turbulent, helical flows produces a large-scale magnetic field that reverses every 11 years. Most alpha-omega solar dynamo models rely on differential rotation in the solar tachocline to generate a strong toroidal field. The most problematic part of such models is then the production of the large-scale poloidal field, via a process known as the alpha-effect. Whilst this is usually attributed to small-scale convective motions under the influence of rotation, the efficiency of this regenerative process has been called into question by some numerical simulations. Motivated by likely conditions within the tachocline, the aim of this paper is to investigate an alternative mechanism for the poloidal field regeneration, namely the magnetic buoyancy instability in a shear-generated, rotating magnetic layer. We use a local, fully compressible model in which an imposed vertical shear winds up an initially vertical magnetic field. The field ultimately becomes buoyantly unstable, and we measure the resulting mean electromotive force (EMF). For sufficiently rapid rotation, we find that a significant component of the mean EMF is aligned with the direction of the mean magnetic field, which is the characteristic feature of the classical alpha-omega-dynamo model. Our results therefore suggest that magnetic buoyancy could contribute directly to the generation of large-scale poloidal field in the Sun.


Publication metadata

Author(s): Duguid CD, Bushby PJ, Wood TS

Publication type: Article

Publication status: Published

Journal: Monthly Notices of the Royal Astronomical Society

Year: 2023

Volume: 520

Issue: 1

Pages: 527-541

Print publication date: 01/03/2023

Online publication date: 14/01/2023

Acceptance date: 12/01/2023

Date deposited: 12/01/2023

ISSN (print): 0035-8711

ISSN (electronic): 1365-2966

Publisher: Oxford University Press

URL: https://doi.org/10.1093/mnras/stad158

DOI: 10.1093/mnras/stad158

ePrints DOI: 10.57711/r7x7-m762


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Funding

Funder referenceFunder name
RPG-2020-109

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